The present, invention relates to an optically variable multilayer film and an optically variable pigment obtained therefrom. The pigment can be mixed with resin or varnish to form color-variable ink or paints so as to be used widely in everyday life.
Optically variable multilayer film is a film which varies colors with the incident angle of light upon the coating. Due to such a characteristic, they have been widely used in advertising boards, documentations and marking labels for anti-counterfeiting and for beautiful purpose.
In the past, attempts making uses of an optical interference technique to provide anti-counterfeiting of valuable stocks have been disclosed in U.S. Pat. No. 3,858,977 (issued to Baird et al). The prior art discloses an optical interference coating comprising a substrate having a colored surface and filter composed of optical multilayers. The color of the filter is varied with the angle of incidence of light onto the filter. The purpose of the colored substrate is to absorb certain light which passed through the filter. In addition, the external surface of the filter is coated with a layer of transparent or colored protective coating. However, this prior art does not disclose the making of pigment or ink with variable colors from the use of optical interference coating film. As a result, the applications of the prior art are rather limited.
U.S. Pat. No. 4,779,898 discloses an optically variable multilayer film coated on an opaque paper currency to achieve an anti-counterfeiting purpose.
The film in the U.S. Patent is deposited with a yellow color hardcoat on the surface. The hardcoat is an acrylic-type polymer added with yellow dye. The major function of the hardcoat is to absorb high angle reflective light of the optical interference coating, such that the coated film varies colors with respect to the incidence light to perform two colors variation. However, the prior art does not disclose the method of forming pigment from the optical interference coating. As a result, the utilization of the prior patent is also rather limited.
U.S. Pat. No. 5,084,351 discloses various applications of an optical interference coated film on anti-counterfeiting and coating aspects and the manufacturing processes of the color-variable printing ink and the pigment. The film is essentially an opaque reflective layer of which both surfaces are deposited symmetrically with period stacks, respectively, such that both the front and rear surface have same color variation. Each group of the period stacks is formed of a dielectric layer and a semi-transparent metallic layer. In the preparation of optically variable multilayer flakes, in this prior art, the optical interference multilayer is coated onto a soluble or insoluble plastic substrate. If the optical interference multilayer film is deposited onto a soluble plastic substrate and a solvent is used to dissolve the substrate, the separation of the substrate from the flakes can not perform thoroughly. That is, the flakes may contaminate by the substrate. This will cause a changed in optical characteristics of multilayer flakes, and the degree of homogeneity if the flakes are to mix with resin to produce ink. If an insoluble plastic substrate is used, a layer of soluble release layer must be deposited before the optical interference film is coated onto the insoluble substrate. The purpose of this is to separate the optical interference coated film from the plastic substrate under water or other kinds of solvents where the release layer can be dissolved. In U.S. Pat. No. 5,084,351, the material of the release layer is a soluble polymer film, for instance acrylic resin, which can be dissolved in ethanol or sodium chloride coated film, which can be dissolved in water. However, these materials lave shortcomings when in use. For instance if the acrylic resin is used as the release layer, the problem of flakes contamination occurs. If sodium chloride coated film is used, it is time-consuming and uneconomical. Besides, when preparing the flakes, the coated film will be corroded by sodium chloride solution. In addition, in the patent, both of the outmost faces of the flake are thin metallic chromium films (the thickness is 10 nm), they are easily affected (such as oxidization) by ambient environment and lost its original glossiness.
As a result of the above drawbacks, it is an object of the present invention to provide an optically variable multilayer film and the preparation method of flakes from the optically variable multilayer film. In accordance with the present invention, the outermost layer of the optically variable multilayer film is coated with a protective layer which is chemically inert. Such a protective layer causes the optically variable multilayer film flake to be capable of being used as a color variation pigment without degradation for long storage.
Another object of the present invention is to provide an optically variable multilayer film and the preparation method of flakes from the optically multilayer film. The flakes in accordance with the present invention are able to be mixed with resin to form color variable ink or paints without causing the formation of a chemical reaction. By coating this material onto papers, the surface of vehicle, advertising board or documents, label and so on, it provides the function of anti-counterfeiting and decoration.
A further object of the present invention is to provide an optically variable multilayer film and the preparation method of flakes from the optically multilayer film in which the color of the flakes will vary with respect to the incident angle of the incident light. If the angle of incidence is about 60.degree. C., no color is observed (achromazation).
It is yet another object of the present invention to provide an optically variable multilayer film and the preparation method of flakes from the optically variable multilayer film, wherein the flakes adhered to the plastic substrate are separated by the use of a release layer. The release a layer is made of a neutral detergent which is soluble in water or organic solvent and is easily dried, non-sticky but easily released. In addition, the release layer will not react chemically with the optically variable multilayer flakes and is manufactured easily and cost-saving suitable for mass production.
Other features and advantages of this invention will be apparent from a consideration of the detailed description in conjunction with the accompanying drawings.